How to Identify a device?

Question

I am implementing an OTP system, where after user credentials are matched then Otp is sent on mobile.

The problem is am looking for a method, by which i can store a device token generated uniquely for each device which will be used to trust that device. So whenever the user logins again then system should not ask again for otp verification for that particular user.
I tried User Agent, ip address but those doesn't seems to work, even mac address could be forged..

So is there any good solution out there for identifying a device to be unique?
Am using Codeigniter4 and mysql database.

Answer 1

Read on Open System Interconnection (OSI). It may help